Where we have been. Cells Organelles Nucleus DNA Replication Chromosomes
Dec 31, 2015
Where we have been.
Cells Organelles
Nucleus DNA
Replication Chromosomes
Let’s Review
Reproduction – 2 types Asexual
Offspring genetically identical to the ONE parent
Quick, many offspring
Sexual Offspring share genetic information from BOTH
parents Creates variation
Curious?
Asexual reproducers Archea Bacteria Protists Starfish
Sexual reproducers (pregnancy length) Birds Humans (9 months) Insects Rabbit (33 Days) Alpine Salamander
(38 months) Elephant (22 months)
Chromosomes
Chromosomes DNA condensed, wrapped around proteins,
called histones Nucleus Only visible during cell division Each organism has its own number
Corn – 20, fruit fly 8, horsetail – 216, Chimp – 48, Dog – 78, humans? Somatic cells? Sex Cells?
Chromosomes
Sister Chromatids The 2 halves of a replicated chromosome
Centromere The place where sister chromatids are
connected
CELL DIVISION
Cell Division
Why? Replace lost cells Repair Growth and development Reproduction
Cell Cycle
“ALL CELLS COME FROM CELLS” The “life cycle” of a cell from the
beginning of one division to the beginning of the next division. The 2 new cells are called Daughter Cells
Cell division 1 cell becomes 2
The Cell Cycle
Interphase G1 – primary growth S – DNA replication G2 – Cell carries out
everyday functions, prepares for division
Mitosis M – Cell divides
Cytokinesis Cytoplasm divides
Starter
1. What is the purpose of cell division?2. What are the 3 major steps and what
happens in each of the cell cycle?3. Why must DNA replication happen
before mitosis and cytokinesis?4. What are the phases of mitosis?5. With a pencil, label your drawings with
the stages of the cell cycle, the phases of mitosis and cytokinesis.
MITOSISThe Break Down
The Phases
Prophase Metaphase Anaphase Telophase Cytokinesis
Prophase
The longest phase Chromatin condenses forming
chromosomes (visible) Centrioles move to opposite sides of the
nucleus Spindle fibers form between them – some
of which attach to centromeres on each side of the chromosome
Nuceolus and nuclear membrane disappear
Metaphase
The shortest phase Chromosomes line up in the center of
the cell Centrioles move to opposite sides of the
cell Spindle fibers are still attached to the
centromeres
Anaphase
Centromeres split Sister chromatids split to make separate
chromosomes Chromosomes move to opposite ends of
the cell This phase ends when the movement
stops
Telophase
Chromosomes begin to uncoil back into chromatin
Nuclear membranes develop around the bundles of chromatin at opposite ends of the cell
Spindle fibers disappear Nucleolus reappear in each new,
daughter cell
Cytokinesis
When the cytoplasm divides, cell division is complete.
Not always the same!
Animals Cell membrane
pinches, forming 2 identical daughter cells
Complete cells that are identical
Plants Cell Plate forms
halfway between the 2 nuclei
Materials for new cell walls and membranes gather and fuse in the middle between the 2 nuclei. Material gradually divides to create 2 cells.